Axially swaged fitting with composite swaging ring

ABSTRACT

A fitting for attachment to a tube by swaging is disclosed. The fitting comprises a cylindrical sleeve having a tapered outer surface and an inner surface for receiving the tube. A cylindrical swaging ring having a tapered inner surface engages the tapered outer surface of the sleeve such that axial movement of the ring in a forward direction with respect to the sleeve causes the ring to apply a radial force to the sleeve to swage it to the tube. The swaging ring is comprised of a lightweight, high strength material, such as a composite material, having high tensile strength in a circumferential direction and a high modulus of elasticity, with relatively low density and low elongation properties. One preferred composite material comprises an epoxy resin matrix and a high strength graphite fiber. The swaging ring is locked onto the sleeve both before and after swaging by one or more protrusions on the outer surface of the sleeve which cooperatively engage an annular groove in the swaging ring.

BACKGROUND OF THE INVENTION

The present invention relates to fluid fittings for connection to tubes and pipes by swaging and, more particularly, to a fitting having an axially movable swaging ring.

Fittings are commonly used to connect metal tubes and pipes to each other for use in a variety of applications, such as in the aerospace industry, to convey fuel, hydraulic control fluids and the like in an aircraft or space vehicle. In these applications, it is critical that there be a secure connection between the fitting and the tubes in order to withstand vibration and other adverse conditions without failure.

Various fittings have been developed in the past to connect tubes to each other. In one type of fitting, a radial swaging force is applied to the fitting and the tube, which may be done externally around the fitting or internally within the tube. In either case, the radial swaging force is applied directly to the fitting and tube by the tool. In some instances, the inner surface of the fitting has a plurality of axially spaced annular grooves into which the material of the tube is deformed by the swaging tool to make the swaged connection. In other instances, a curved or irregular configuration on the outer surface of the fitting is transferred to the inner surface of the fitting upon swaging, which causes the tube to deflect and conform to the irregular configuration and thereby make the connection.

Another type of fitting comprises a cylindrical sleeve having a tapered outer surface and a cylindrical inner surface for receiving a tube. A deforming ring surrounds the sleeve and has a tapered inner surface which matches and engages with the tapered outer surface of the sleeve. Before swaging, the deforming ring is positioned outwardly with respect to the sleeve such that no radial force is applied by the deforming ring to the sleeve. During swaging, the deforming ring is moved axially in a forward direction over the sleeve such that the interaction of the tapered surfaces on the ring and the sleeve applies a radial force deforming the sleeve and the tube inwardly to make a swaged connection between them. These fittings shall be generally referred to as axially swaged fittings.

In the aircraft industry and in the marine and commercial fields, it is desirable to have the weight of the hydraulic plumbing installation as low as possible. All of the fittings described above pose a problem in this regard, since many hundreds of them are used in an aircraft, thus making their total weight contribution a noticeable amount. Because of the high flexure and operating pressures in the tubes, the fittings are made of metal and generally must be sufficiently large in both size and weight to resist fatigue failure and to ensure adequate holding power and tube retention capability. As a result, most fittings in use today are relatively large and heavy and, therefore, add undesirable weight to the aircraft. Since axially swaged fittings have a deforming ring, which remains as a permanent part of the swaged fitting, these fittings tend to add extra undesirable weight.

Another problem which especially concerns axially swaged fittings is the inability to conveniently hold the deforming ring onto the sleeve prior to swaging, and then to securely lock the ring to the sleeve after swaging. In some instances, the deforming ring is preassembled onto the sleeve and held there by frictional engagement or other means. However, if the frictional engagement is insufficient, the deforming ring may become separated from the sleeve and sometimes lost or damaged. If the frictional engagement is too great, however, the outer end of the sleeve may be radially pre-deformed to such an extent that the tubing will not fit within the radially constricted sleeve. In other instances, the deforming ring is simply loosely packaged with the sleeve and subject to loss or damage or, even worse, the ring may be incorrectly installed when placed over the sleeve.

Accordingly, there has existed a definite need for an axially swaged fitting that is smaller in size and lighter in weight than the known fittings, while still maintaining a high tube retention capability. There has further existed a definite need for an axially swaged fitting in which the deforming ring is securely attached to the swaging sleeve prior to swaging, without permanently deforming the sleeve's tube insertion diameter, and in which the ring is positively locked to the sleeve after swaging. The present invention satisfies these and other needs and provides further related advantages.

SUMMARY OF THE INVENTION

The present invention is embodied in a compact and lightweight fitting having a high tube retention capability. The fitting comprises a substantially cylindrical sleeve having a tapered outer surface and an inner surface defining an axial bore for receiving the tube at an outer end of the sleeve. The inner surface of the cylindrical sleeve includes a plurality of axially spaced annular grooves into which the outer surface tube deforms upon swaging. A substantially cylindrical swaging ring having a tapered inner surface is adapted to engage the tapered outer surface of the sleeve. Axial movement of the ring in a forward direction with respect to the sleeve therefore causes the ring to apply a radial force to the sleeve which swages the sleeve to the tube.

More particularly, the swaging ring comprises a two-piece ring assembly In this form of the invention, the ring assembly comprises a swaging insert having an outer end, a cylindrical outer surface and a tapered inner surface adapted to engage the tapered outer surface of the sleeve. The ring assembly also comprises a substantially cylindrical swaging ring made of a lightweight, high strength material, such as a composite material, having an inner surface adapted to engage the outer surface of the insert. Axial movement of the ring assembly with respect to the sleeve causes the ring assembly to apply a radial force to the sleeve to swage it to the tube.

In another form of the invention, the swaging ring comprises a one-piece swaging ring made of composite or similar high strength material. The configuration of the ring in this embodiment is essentially the same as the combined configuration of the insert and ring of the two-piece ring assembly described above.

In accordance with the invention, the swaging ring preferably is comprised of a composite material making the swaging ring as lightweight as possible. The composite material or other suitable material has special characteristics for use as a swaging ring, including a relatively high tensile strength which is greater than about 180,000 psi in a circumferential direction and a relatively high modulus of elasticity which is greater than about 15,000,000 psi. In addition, the material preferably has a density of less than about 0.080 pound per cubic inch. In one embodiment, the composite material comprises an epoxy resin matrix, such as bisphenol type A epoxy resin, in combination with high strength graphite fiber. The fibers comprising the high strength graphite fiber are oriented substantially in a circumferential direction around the ring. This combination of features gives the swaging ring characteristics exceeding those described above to provide high tube retention capability, yet providing the most lightweight fitting possible.

In one aspect of the invention, the epoxy resin has a tensile strength of at least 5,000 psi and a modulus of elasticity of at least 500 psi and, preferably, has a tensile strength of between approximately 5,000 to 12,000 psi and a modulus of between approximately 500 to 1,200 psi. Similarly, the high strength graphite fiber has a tensile strength of at least 200,000 psi and a modulus of elasticity of at least 10,000,000 psi and, preferably, a tensile strength of between approximately 200,000 to 20,000,000 psi and a modulus of approximately 10,000,000 to 150,000,000 psi. As noted above, the swaging ring also has a relatively low density, preferably between 0.050 to 0.080 pound per cubic inch, and low elongation, preferably between approximate to 0.003 to 0.020 inch/inch.

In another aspect of the invention, the swaging ring is advantageously locked onto the sleeve both before and after swaging. This is accomplished by first and second annular protrusions spaced axially from each other on the outer surface of the sleeve. An annular groove on the inner surface of the swaging ring positively engages the first annular protrusion to hold the ring onto the sleeve before swaging, without constricting the diameter of the sleeve. During swaging, the second annular protrusion and the sleeve are deformed radially inward. After swaging, the second annular protrusion springs back into and engages the annular groove to form a lock inhibiting relative axial movement in a reverse direction between the ring and the sleeve.

In another embodiment of the invention, a single annular protrusion on the outer surface of the sleeve positively engages an annular groove on the inner surface of the swaging ring prior to swaging to hold the ring in place. After swaging, the outer end of the ring will have been moved axially in the forward direction just past the annular protrusion. This permits the protrusion to engage the outer end of the ring to form a mechanical lock inhibiting relative axial movement in a reverse direction between the ring and the sleeve.

Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a cross-sectional elevational view of one embodiment of a fitting embodying the novel features of the present invention and shown connecting two tubes to each other;

FIG. 2 is an enlarged cross-sectional view of a portion of the fitting, showing a tube inserted into one end of the fitting prior to swaging;

FIG. 3 is an enlarged cross-sectional view of the fitting, similar to FIG. 2, showing the fitting and the tube after the swaging operation has been completed;

FIG. 4 is an enlarged and isolated cross-sectional view of a portion of the fitting showing the manner in which a swaging ring is positively connected to a sleeve of the fitting prior to swaging;

FIG. 5 is another enlarged and isolated crosssectional view, similar to FIG. 4, showing the manner in which the swaging ring is locked to the sleeve after swaging;

FIG. 6 is a cross-sectional elevational view of a portion of another embodiment of a fitting embodying the novel features of the present invention and shown connecting two tubes to each other;

FIG. 7 is an enlarged cross-sectional view of a portion of the fitting, showing a tube inserted into one end of the fitting prior to swaging;

FIG. 8 is an enlarged cross-sectional view of the fitting, similar to FIG. 7, showing the fitting and the tube after the swaging operation has been completed;

FIG. 9 is an enlarged and isolated cross-sectional view of a portion of the fitting illustrating the manner in which a swaging ring assembly is positively connected to a sleeve of the fitting prior to swaging;

FIG. 10 is an enlarged and isolated cross-sectional view, similar to FIG. 9, showing the manner in which the swaging ring assembly is locked to the sleeve after swaging;

FIG. 11 is an elevational view of a mechanism for the material used to make the swaging ring;

FIG. 12 is a cross-sectional view of the swaging ring, showing the alignment in a circumferential direction of high strength composite fibers used to construct the ring; and

FIG. 13 is an enlarged cross-sectional view showing an alternative embodiment of the swaging ring assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the accompanying drawings, the present invention is embodied in a fitting, indicated generally by the reference number 10, for use in connecting two tubes 12 and 14 to each other. The fitting 10 comprises a substantially cylindrical sleeve 16 having an outer surface 18 and an inner surface 20 defining an axial bore for receiving the tubes 12 and 14. The fitting 10 is relatively compact and lightweight, yet it has a higher tube retention capability than bulkier and heavier fittings used for the same purpose. As explained in more detail below, these advantages are provided by a swaging ring assembly 22 having a swaging insert 24 and a special swaging ring 26 constructed from a lightweight, high strength material, such as a composite material.

As shown best in FIG. 1, the fitting 10 has a symmetrical configuration on opposite sides of an annular groove 28 which essentially divides the fitting 10 into two separate but identical portions. For ease of reference and clarity, only one of these portions will be described, since it is understood that the other portion of the fitting 10 is structurally and functionally the same. It also should be understood that, depending on the particular application for the fitting 10, a complete fitting may comprise only one of the two portions. For example, the fitting 10 may comprise an end cap to close off the end of a tube. Alternatively, the fitting 10 may provide some other coupling function, such as a tee, cross-fitting, elbow or a reducer, in which case two or more portions of the fitting would be needed to connect multiple tubes.

FIGS. 2-3 show the sleeve 16 and ring assembly 22 in closer detail. More particularly, the outer surface 18 of the sleeve 16 has a tapered region 30 near its outer end 32 and a substantially cylindrical region 34 spaced inwardly from the outer end 32, terminating in an annular ring stop 36 at the inner end of the sleeve 16. The inner surface 20 of the sleeve 16 has two or more axially spaced annular grooves 38 and 40 into which the material of the tube 12 is deformed upon swaging. The use of these annular grooves 38 and 40 is well known and, therefore, will not be described in further detail. However, it should be understood that other means for causing the sleeve 16 to securely engage the tube 12 after swaging may be used, and the particular means shown in the drawings, in this case the axially spaced annular grooves 38 and 40, should not be construed as limiting the claimed invention. For example, it is also known that a curved or irregular configuration may be used on the sleeve 16 instead of axially spaced annular grooves 38 and 40. In these latter applications, the tube 12 is deflected and conforms to the curved or irregular configuration of the sleeve 16 during the swaging process to make the swaged connection. Various other means for forming a secure connection between the sleeve 16 and the tube 12 upon swaging will be apparent to those skilled in the art.

Swaging of the sleeve 16 to the tube 12 is caused by axial movement of the ring assembly 22 in a forward direction (to the right in the drawings), as shown in FIGS. 2-3. FIGS. 1-2 also show the pre-swaging position of the ring assembly 22 in phantom lines 42. As noted above, the ring assembly 22 comprises the swaging insert 24 and the swaging ring 26. The swaging insert 24 comprises a substantially cylindrical body with an outer end in the form of a flange 46 extending radially outward. The insert 24 also has a cylindrical outer surface 48 and a cylindrical inner surface 52 with a tapered region 50 adapted to match with and engage the tapered region 30 of the sleeve 16. The angle of the tapered region 30 on sleeve 16 and the tapered region 50 on the insert 24 is approximately 5 degrees, but it may be at any other appropriate angle. The swaging ring 26 is substantially cylindrical and has an inner surface 58 adapted to engage with and fit against the outer surface 48 and flange 46 of the insert.

To swage the sleeve 16 to the tube 12, the ring assembly 22 is moved axially in the forward direction from the position shown in FIG. 2 to the position shown in FIG. 3. This axial movement of the ring assembly 22 with respect to the sleeve 16, as a result of the interaction between the tapered regions 30 and 50 on the sleeve 16 and insert 24, respectively, causes the ring assembly 22 to apply a radial force to the sleeve 16. This radial force swages the sleeve 16 to the tube 12 to form the necessary connection. Movement of the ring assembly 22 in the forward direction may be accomplished by a swaging tool (not shown) having a pair of jaws which engage the flange 46 on the insert 24 and a vertical surface 60 on the ring stop 36. The jaw engaging the ring stop 36 remains stationary, while the jaw engaging the flange 46 is moved axially toward the other jaw. Alternatively, the jaw engaging the ring stop 36 may move and the jaw engaging the flange may be stationary. Movement of the jaws in this manner may be carried out by hydraulic, pneumatic or other appropriate means. In any event, at the conclusion of the swaging operation, the material of the tube 12 will have deformed generally into an hour glass shape, as shown in FIG. 3, and will have locally deformed into the axially spaced annular grooves 38 and 40 on the inner surface 20 of the sleeve 16, thereby forming a secure swaged connection.

In accordance with the invention, the ring 26 is constructed from a lightweight, high strength material having relatively high tensile strength and a high modulus of elasticity, with relatively low density and low elongation properties. In the preferred embodiment, the material is a composite material comprising an epoxy resin matrix which is reinforced by high strength graphite fibers 64. (FIGS. 11-12). These graphite fibers 64 are tightly packed within the epoxy resin matrix and are oriented in a circumferential direction around the ring 26 in a continuous fashion, as shown in FIG. 12. The strength properties of the composite material may be varied as desired and are dependent upon factors such as fiber density and fiber orientation within the epoxy resin matrix. For purposes of the present invention, the following properties have been found to be suitable for materials used in constructing the composite swaging ring 26.

In one preferred form, the epoxy resin has a tensile strength of at least 5,000 psi and a modulus of elasticity of at least 500 psi and, preferably, a tensile strength of between approximately 5,000 to 12,000 psi and a modulus of between approximately 500 to 1,200 psi. An epoxy resin having these preferred properties is bisphenol type A epoxy resin available from Advanced Composite Products & Technology of Huntington Beach, California. Similarly, the high strength graphite fiber preferably has a tensile strength of at least 200,000 psi and a modulus of elasticity of at least 10,000,000 psi and, preferably, a tensile strength of between approximately 200,000 to 20,000,000 psi and a modulus of between approximately 10,000,000 to 150,000,000 psi. High strength graphite fiber having these properties also is available from Advanced Composite Products & Technology Inc. of Huntington Beach, California. A fully constructed composite swaging ring 26 having the properties described above preferably has a tensile strength which is greater than about 180,000 psi, a modulus of elasticity which is greater than about 15,000,000 psi, a density of between approximately to 0.050 to 0.080 pound per cubic inch and elongation of between approximate 0.003 to 0.020 inch/inch. A preferred material for both the sleeve 16 and the swaging insert 24 is titanium, such as 6AL-4V titanium available from Titanium Sales of Cerritos, California.

The structural relationship between the insert 24 and the ring 26 described above provides important advantages in terms of function and operation of the fitting 10. The insert 24, which preferably is made of titanium, has relatively high strength to resist shear and bearing loads, and relatively high tensile strength in the axial direction. This allows the insert 24 to withstand high loads of shear and bearing which are generated when the insert 24 is moved over the sleeve 16 during swaging. However, the insert 24 has relatively low tensile strength in the circumferential (hoop) direction. This is where the swaging ring 26 becomes important.

The swaging ring 26, which is preferably constructed from the high strength composite materials described above, provides an ideal back-up of the insert 24 in the circumferential direction. This is because of the ring's relatively high tensile strength in the circumferential direction, which allows it to withstand high hoop swaging loads which occur during swaging. These hoop loads are first generated in the insert 24 and then transferred mostly to the ring 26. This load transfer takes place because of the difference in modulus of elasticity between the insert 24 and the ring 26. Since the modulus of the ring 26 preferably is roughly twice that of the insert 24, as soon as the insert 24 starts to deform radially outwardly, it becomes constrained by the swaging ring 26 with its higher modulus of elasticity, low elongation properties and high tensile strength in the circumferential direction. Although the ring 26 is relatively weak to resist shear and bearing loads, and in its axial tensile strength, its outstanding strengths in the other areas compliment the insert 24 to provide a combination of structural and functional features enabling the high tube retention capability and high tube operating pressure.

By varying the properties of the material forming the swaging ring 26, the ring can be optimized to such an extent that it may be used alone, without the swaging insert 24. In this aspect of the invention, the two-piece swaging ring assembly 22 described above is substituted for a one-piece swaging ring assembly, comprising only the swaging ring 26, but having the combined structural configuration of the two-piece assembly 22. Since the ring 26 must now also serve the function of the swaging insert 24, the inner surface of the ring 26 must have sufficient hardness at the swaging interface, as well as sufficient tensile strength in the circumferential direction. Moderate shear strength also L must be provided. This can be achieved by using a composite material with a helical winding of fibers 64 such that the inner surface of the ring 26 meets the requirements of strength and hardness in an optimal manner.

In this regard, FIG. 11 shows an apparatus such as a mandrel 62 for winding of the composite material to form the swaging ring 26. To form the helical winding, the winding angle for the composite fibers 64 is less than 90 degrees, and preferably no less than 45 degrees, at the inner surface of the ring 26. Thus, the initial layers of the fiber are wound at a first angle α₁ of about 45 degrees. Subsequent layers of the composite fiber 64 approaching the outer surface of the ring 26 may be wound at a greater angle α₂ approaching 90 degrees. The same mandrel 62 may be used to wind the composite fibers 64 used to form the ring 26 of the two-piece ring assembly 22. In the two-piece ring assembly 22, however, the composite fibers preferably are wound at an angle α₂ closely approaching 90 degrees throughout the layers of the ring 26. This is because high strength to resist shear, bearing and tensile loads in the axial direction is not needed in the swaging ring 26, since that is supplied by the insert 24. Hence, the near 90 winding angle α₂ for the composite fibers provides the highest circumferential tensile strength and modulus of elasticity.

Thus, it will be appreciated that appropriate fiber orientation may be varied as desired to provide the maximum possible tensile strength in the circumferential direction, while providing the required hardness and shear strength at the swaging interface when desired. In this regard, FIG. 12 shows the preferred orientation of the graphite fibers 64 in the swaging ring 26. It is noted that these fibers 64 are substantially all oriented in a circumferential direction around the ring 26.

FIGS. 4-5, and to a lesser extent FIGS. 2-3, illustrate a method for locking the swaging ring assembly 22 onto the sleeve 16 both before and after swaging. This locking feature is accomplished by providing an annular protrusion 66 on the outer surface 18 of the sleeve 16, in the area of the sleeve's tapered region 30, which is adapted to engage an annular groove 68 on the inner surface 52 of the swaging insert 24 in the area of its tapered region 50. Before swaging, therefore, and during pre-assembly of the fitting 10 prior to shipping, the ring assembly 22 may be pushed onto the outer end 32 of the sleeve 16, deforming the annular protrusion 66 until the annular protrusion 66 on the sleeve 16 engages the annular groove 68 in the ring assembly 22. The location of the protrusion 66 and the groove 68 are such that little or no radial force is applied by the ring assembly 22 to the sleeve 16. Later, during swaging, the ring assembly 22 is moved axially with respect to the sleeve 16, deforming the annular protrusion 66, until the forward end of the ring assembly 22 engages the curved surface 72 of the ring stop 36. This ends the swaging operation, at which point the flange 46 at the outer end of the ring assembly 22 will have been moved axially in the forward direction just past the annular protrusion 66. When the swaging tool (not shown) is removed, the frictional engagement between the ring assembly 22 and the sleeve 16 at the swaging interface inhibits reverse movement of the ring assembly 22. However, the protrusion 66, which springs back from its deformed condition when the ring assembly 22 passes over it, functions as a stop which engages the flange 46 at the outer end of the ring assembly 22 to form a lock that further inhibits reverse movement of the ring assembly. Thus, positive mechanical engagement between the outer end of the ring assembly 22 and the protrusion 66 maintains a reliable swaged connection between the sleeve 16 and the tube 12.

FIGS. 6-10 show another embodiment of the fitting 10. This fitting 10 has essentially the same structural and functional properties of the fitting 10 described above in connection with FIGS. 1-5. However, it will be noted that the two-piece ring assembly 22 is longer in the axial direction and the composite ring 26 is somewhat thinner in the radial direction. The fitting 10 also employs a somewhat different mechanism for locking the ring assembly 22 onto the sleeve 16 prior to and after swaging.

As shown best in FIGS. 9-10, and to a lesser extent in FIGS. 7-8, the ring assembly 22 is locked onto the sleeve 16, both before and after swaging, by two axially spaced annular protrusions 74 and 76 on the outer surface 18 of the sleeve 16. The first annular protrusion 74 is adjacent to the outer end 32 of the sleeve 16 on its tapered region 30, and the second annular protrusion 76 is spaced inwardly on the cylindrical region 34 of the sleeve 16. An annular groove 78 on the tapered region 50 of the swaging insert's inner surface 52 is adapted to engage the first annular protrusion 74 to hold the ring assembly 22 onto the sleeve 16 before swaging without deforming or constricting the sleeve.

During swaging, the tapered region 50 on the insert 24, in a location forward of the annular groove 78, passes over the second annular protrusion 76 and elastically deforms it in a radially inward direction. Advancement of the swaging ring assembly 22 in the forward direction continues until the forward end of the ring assembly 22 engages the curved surface 72 of the ring stop 36. This ends the swaging operation, at which point the annular groove 78 will have reached the second annular protrusion 76, where the protrusion 76 is allowed to spring back into the groove 78. Hence, the protrusion 76 is deformed radially outwardly into the groove 78 of the insert 24, thereby creating a positive locking relationship between the sleeve 16 and the ring assembly 22 that, in addition to the frictional engagement between these two components at the swaging interface, inhibits axial movement of the ring assembly 22 in a reverse direction over the sleeve 16.

The spring back of the protrusion 76 also deforms the material of the insert 24 radially outward into a groove 80 of the swaging ring 26. Another annular groove 82 also is provided on the inner surface of the swaging ring 26 to facilitate assembly of the fitting 10, so that either end of the ring 26 can be assembled onto the insert 24. This prevents the ring 26 from being incorrectly installed on the insert 24.

In both embodiments of the fitting 10 described above, the protrusions 66 and 76 advantageously provide a surface forming an angle of about 45 degrees or greater with respect to the longitudinal axis of the sleeve for engagement with the annular grooves 68 and 78. This relatively high ramp angle of the protrusions 66 and 76, in combination with the spring back properties of the sleeve 16, substantially inhibit axial movement of the ring assembly 22 in a reverse direction over the sleeve 16. This is a significant advantage as compared to prior art fittings which have relatively low ramp angles, usually less than about 2 degrees, and which depend primarily upon the natural spring back contour generated by the tube and outer end of the sleeve, to the extent that the sleeve extends beyond the outer end of the swaging ring, to hold the ring in a locked position.

The embodiment of the fitting 10 in FIGS. 6-10 also provides a locking relationship between the swaging ring 26 and the swaging insert 24. At the end of the swaging operation, as noted above, the material of the insert 24 will have been deformed into the groove 80. This provides high contact pressure which results in a secure connection preventing both axial and circumferential movement of the ring 26 with respect to the insert 24. This holds the ring assembly 22 in position so that it can withstand the types of environments encountered in service. In this regard, should the swaging ring 26 somehow become removed from the fitting, either partially or wholly as a result of corrosion or other means, the material of the swaging insert 24 has the necessary strength characteristics to maintain a swaged and secure connection between the sleeve 16 and the tube 12.

FIG. 13 shows another embodiment of the fitting 10, in which the inner surface 58 of the swaging ring 26 does not have any annular grooves 80 or 82 as in FIG. 8. Instead, an annular groove 84 is provided on the outer surface 48 of the insert 24. In this embodiment, the groove 84 is radially aligned with the annular groove 78 on the inner surface 52 of the insert 24. Thus, at the end of the swaging operation, when the protrusion 76 on the sleeve 16 springs back into the annular groove 78 on the insert 24, the material of the insert 24 can be deformed radially into the annular space defined by the groove 84.

From the foregoing, it will be appreciated that the fitting 10 of this invention provides high tube retention capability and reliability, while still being extremely compact and lightweight in character. Moreover, prior to swaging, the ring assembly 22 is positively secured to the sleeve 16 to prevent loss or damage, and after swaging, it is securely locked onto the sleeve 16 to maintain its position and ensure a strong and secure connection.

While a particular form of the invention has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims. 

We claim:
 1. A fitting for attachment to a tube by swaging, comprising:(a) a substantially cylindrical sleeve having a tapered outer surface and an inner surface defining an axial bore for receiving the tube at an outer end of the sleeve; (b) means on the sleeve adapted to form a secure connection between the sleeve and the tube upon swaging; and (c) a substantially cylindrical swaging ring having a tapered inner surface adapted to engage the tapered outer surface of the sleeve such that axial movement of the ring in a forward direction with respect to the sleeve causes the ring to apply a radial force to the sleeve to thereby swage the sleeve to the tube, wherein at least a portion of the ring surrounding the tapered inner surface is comprised of a lightweight, high strength material having a relatively high tensile strength in a circumferential direction and a comparatively low tensile strength in an axial direction.
 2. The fitting of claim 1, wherein said portion of the swaging ring is comprised of a low density, high strength material having a density of less than about 0.080 pound per cubic inch, a tensile strength of greater than about 200,000 psi and a modulus of elasticity of greater than about 15,000,000 psi.
 3. The fitting of claim 2, wherein the material comprising said portion of the ring is a composite material.
 4. The fitting of claim 3, wherein the composite material comprises an epoxy resin matrix and high strength graphite fiber.
 5. The fitting of claim 4, wherein the epoxy resin comprises bisphenol type A epoxy resin having a tensile strength of between approximately 5,000 to 12,000 psi and a modulus of elasticity of between approximately 500 to 1,200 psi.
 6. The fitting of claim 4, wherein the fibers comprising the high strength graphite fiber are oriented substantially in a circumferential direction around the ring.
 7. The fitting of claim 4, wherein the density of said portion of the ring is between approximately 0.050 to 0.080 pound per cubic inch and the elongation is between approximately 0.003 to 0.020 inch/inch.
 8. The fitting of claim 4, wherein the epoxy resin has a tensile strength of at least 5,000 psi and a modulus of elasticity of at least 500 psi.
 9. The fitting of claim 8, wherein the high strength graphite fiber has a tensile strength of at least 200,0000 psi and a modulus of elasticity of at least 10,000,000 psi.
 10. The fitting of claim 8, wherein the high strength graphite fiber has a tensile strength of between approximately 200,000 to 20,000,000 psi and a modulus of elasticity of between approximately 10,000,000 to 150,000,000 psi.
 11. The fitting of claim 1, further comprising locking means for locking the swaging ring to the sleeve prior to swaging, wherein the locking means does not cause permanent radial deformation of the sleeve to an extent that interferes with insertion of the tube into the sleeve prior to swaging.
 12. The fitting of claim 11, wherein the locking means comprises a first annular protrusion on the outer surface of the sleeve and an annular groove on the inner surface of the swaging ring adapted to engage the first annular protrusion to hold the ring onto the sleeve before swaging.
 13. The fitting of claim 1, further comprising locking means for locking the swaging ring to the sleeve after swaging, wherein the locking means comprises an annular groove on the inner surface of the swaging ring and an annular protrusion on the outer surface of the sleeve such that, during swaging, the annular protrusion is deformed radially inwardly by the swaging ring and, after swaging, the annular protrusion is adapted to spring back into the annular groove to form a lock inhibiting relative axial movement in a reverse direction between the ring and the sleeve.
 14. The fitting of claim 13, wherein the annular protrusion provides a surface having an angle of at least 45 degrees relative to the longitudinal axis of the sleeve.
 15. The fitting of claim 1, further comprising locking means for locking the swaging ring to the sleeve after swaging, wherein the locking means comprises an annular protrusion on the outer surface of the sleeve such that, during swaging, the annular protrusion to spring back and engage said one end of the ring to form a lock inhibiting relative axial movement in a reverse direction between the ring and the sleeve.
 16. The fitting of claim 15, wherein the annular protrusion provides a surface having an angle of at least 45 degrees relative to the longitudinal axis of the sleeve.
 17. The fitting of claim 1, wherein the swaging ring comprises a two-piece ring assembly, comprising:(a) a swaging insert having a substantially cylindrical body with an outer end, an outer surface and a tapered inner surface adapted to engage the tapered outer surface of the sleeve; and said at least a portion is (b) a substantially cylindrical swaging ring having an inner surface engaging the outer surface of the cylindrical body, wherein the ring is comprised of a lightweight, high strength material having relatively high tensile strength in a circumferential direction and a relatively high modulus of elasticity, with relatively low density and elongation properties, such that axial movement of the ring assembly with respect to the sleeve in said forward direction causes the ring assembly to apply a radial force to the sleeve to thereby swage the sleeve to the tube.
 18. The fitting of claim 17, wherein the insert is comprised of a material having relatively high shear, bearing and axial strength.
 19. The fitting of claim 17, wherein the insert is comprised of titanium.
 20. The fitting of claim 17, wherein the inner surface of the swaging ring has at least one annular groove into which the material of the swaging insert deforms during swaging of the fitting to the tube.
 21. The fitting of claim 18, wherein one end of the insert has an annular flange extending radially outwardly from the outer end of the body for engagement by a swaging tool to move the ring assembly in said forward direction during swaging of the fitting to the tube.
 22. A fitting for attachment to a tube by swaging, comprising:(a) a substantially cylindrical sleeve having a tapered outer surface and an inner surface defining an axial bore for receiving the tube at an outer end of the sleeve; (b) means on the sleeve adapted to form a secure connection between the sleeve and the tube upon swaging; (c) a substantially cylindrical swaging ring having a tapered inner surface adapted to engage the tapered outer surface of the sleeve such that axial movement of the ring in a forward direction with respect to the sleeve causes the ring to apply a radial force to the sleeve to thereby swage the sleeve to the tube; (d) an annular protrusion on the outer surface of the sleeve; and (e) an annular groove on the inner surface of the swaging ring engaging the annular protrusion to hold the ring onto the sleeve before swaging, the ring being moved axially with respect to the sleeve during swaging such that, during swaging the ring deforms the annular protrusion radially inwardly and, at the end of the swaging operation, one end of the ring will have been moved axially in said forward direction past the annular. protrusion, whereby the annular protrusion springs back and engages said one end of the ring to form a lock inhibiting relative axial movement in a reverse direction between the ring and the sleeve.
 23. A fitting for attachment to a tube by swaging, comprising:(a) a substantially cylindrical sleeve having a tapered outer surface and an inner surface defining an axial bore for receiving the tube at an outer end of the sleeve; (b) means on the sleeve adapted to form a secure connection between the sleeve and the tube upon swaging; (c) a substantially cylindrical swaging ring having a tapered inner surface adapted to engage the tapered outer surface of the sleeve such that axial movement of the ring in a forward direction with respect to the sleeve causes the ring to apply a radial force to the sleeve to thereby swage the sleeve to the tube; (d) a first annular protrusion on the outer surface of the sleeve; (e) a second annular protrusion on the outer surface of the sleeve that is axially spaced from the first annular protrusion; and (f) an annular groove on the inner surface of the swaging ring engaging the first annular protrusion to hold the ring onto the sleeve before swaging, and to engage the second annular protrusion to form a lock inhibiting relative axial movement in a reverse direction between the ring and the sleeve after completion of swaging, wherein the first annular protrusion is deformed radially inward during and after swaging to cause the sleeve to apply further radial gripping forces to the tube whereby said sleeve and the tube reach maximum deformation intermediate said protrusions.
 24. The fitting of claim 23, wherein the swaging ring is comprised of a lightweight, high strength material having relative high tensile strength in a circumferential direction and a relatively high modulus, with relatively low density and low elongation properties.
 25. The fitting of claim 24, wherein the swaging ring is comprised of a composite material including an epoxy resin matrix and high strength graphite fiber.
 26. The fitting of claim 24, wherein the swaging ring comprises a ring assembly, comprising:(a) a swaging insert having a substantially cylindrical body with an outer end, an outer surface and a tapered inner surface adapted to engage the tapered outer surface of the sleeve; and (b) a substantially cylindrical swaging ring having an inner surface engaging the outer surface of the cylindrical body, wherein the ring is comprised of a composite material having relatively high fiber tensile strength in a circumferential direction and a relatively high fiber modulus, with relatively low density and elongation properties, such that axial movement of the ring assembly with respect to the sleeve in said forward direction causes the ring assembly to apply a radial force to the sleeve to thereby swage the sleeve to the tube.
 27. The fitting of claim 26, wherein the insert is comprised of titanium.
 28. A fitting for attachment to a tube by swaging, comprising:(a) a substantially cylindrical sleeve having a tapered outer surface and an inner surface defining an axial bore for receiving the tube at an outer end of the sleeve; (b) means on the sleeve adapted to form a secure connection between the sleeve and the tube upon swaging; and (c) a two-piece ring assembly, comprising,a swaging insert having a substantially cylindrical body with an outer end, an outer surface and a tapered inner surface adapted to engage the tapered outer surface of the sleeve, and a substantially cylindrical swaging ring having an inner surface engaging the outer surface of the swaging insert's cylindrical body, wherein the swaging ring is comprised of a lightweight, high strength material having relatively high tensile strength in a circumferential direction and comparatively low tensile strength in an axial direction, such that axial movement of the ring assembly with respect to the sleeve in a forward direction causes the ring assembly to apply a radial force to the sleeve to thereby swage the sleeve to the tube.
 29. A fitting for attachment to a tube by swaging, comprising:(a) a substantially cylindrical sleeve having a tapered outer surface and an inner surface defining an axial bore for receiving the tube at an outer end of the sleeve; (b) means on the sleeve adapted to form a secure connection between the sleeve and the tube upon swaging; and (c) a substantially cylindrical swaging ring having a tapered inner surface adapted to engage the tapered outer surface of the sleeve such that axial movement of the ring in a forward direction with respect to the sleeve causes the ring to apply a radial force to the sleeve to thereby swage the sleeve to the tube, wherein the ring is comprised of,an inner layer formed of a material having strength sufficient to resist shear, bearing and tensile loads in an axial direction that are generated during swaging between the sleeve and the swaging ring, and an outer layer engaging and surrounding the inner layer, wherein the outer layer is formed of a material having a relatively high strength to resist tensile loads in a circumferential direction, wherein the material comprising the outer layer has strength characteristics that are different from the strength characteristics of the material comprising the inner layer, such that the outer layer can withstand substantially higher tensile loads in the circumferential direction than the inner layer, and the inner layer can withstand higher shear, bearing and tensile loads in the axial direction than the outer layer. 